Self-contained hydraulic lash adjuster

ABSTRACT

A self-contained hydraulic lash adjuster which does not depend upon any external source of hydraulic fluid in operation is used in the valve trains of internal combustion engines or similar mechanisms in order to take up the lash or operating clearance in the valve trains. In the lash adjuster a transmitting member such as a fulcrum is engaged with a plunger which is slidably mounted in a bore of a lash adjuster body. A clearance is provided between the transmitting member and the body which is smaller than the clearance provided between the transmitting member and the plunger to reduce the frictional wear between the plunger and the body.

This is a continuation, of application Ser. No. 31,092, filed Apr. 18,1979, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hydraulic lash adjusters as used in the valvetrains of internal combustion engines or similar mechanisms and moreparticularly to hydraulic lash adjusters of the self-contained type inwhich the fluid is sealed within the assembly with no provision for itsreplacement from any external source during operation.

2. Prior Art

The conventional lash adjuster of this type comprises a cylindrical bodywith a blind bore and a plunger slidably mounted in the blind bore. Whenthe plunger is moved in the axial direction by the force applied theretothrough a transmitting member such as a fulcrum in engagement therewith,the plunger is simultaneously urged to move in the radial direction ofthe body and the outer surface of the plunger is brought into contactwith the inner surface of the body by a component of the force since thedirection of the force does not correspond to the axis of the plunger.Between the inner surface of the body and the outer surface of theplunger, there is provided a leakage clearance through which a verysmall amount of silicone oil passes. Since the silicone oil has littleor no lubricating effect, the inner surface of the body and the outersurface of the plunger will be subjected to frictional wear therebydecreasing the accuracy of the lash adjuster in operation.

SUMMARY OF THE INVENTION

The present invention provides a new and improved hydraulic lashadjuster which will overcome the above-mentioned drawbacks.

The present invention provides a new and improved hydraulic lashadjuster wherein uneven frictional wear between the vertically movableplunger and the cylindrical body is avoided thereby ensuring theaccurate operation of the lash adjuster.

The present invention provides a new and improved hydraulic lashadjuster which is simple in construction and is inexpensive in cost.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following description of a preferredembodiment with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transverse sectional view through a portion of an internalcombustion engine having a valve operating train incorporating anhydraulic lash adjuster constructed in accordance with the presentinvention.

FIG. 2 is an enlarged longitudinal sectional view through the lashadjuster of FIG. 1 showing the internal construction in detail.

FIG. 3 is a sectional view through the lash adjuster taken along theline III--III of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the drawings, there is illustrated in FIG. 1an internal combustion engine having a cylinder block 10 containing abore 11 in which a piston 12 is reciprocably mounted. The engineincludes a cylinder head 13 secured to the top of the cylinder block 10thereby forming a combustion chamber 14 above the piston 12.

The communication between the combustion chamber 14 and a head port 15is controlled by a poppet valve 16 which cooperates with a seat 21. Thevalve 16 has a stem 18 slidably mounted for reciprocation in thecylinder head 13. A valve return spring comprised of a helical tortionspring surrounding the valve stem 18 is disposed between a spring seat17 on the cylinder head 13 and a retainer 19 fixed to the upper end ofthe valve stem 18. The spring 20 serves to maintain the valve 16normally in its closed position as illustrated in FIG. 1.

The cylinder head 13 is further provided with a cylindrical blind bore23 in which a lash adjuster 30 according to the present invention isfitted. A fulcrum 47 is engaged with one end 22b of a rocker arm 22. Theother end 22a of the rocker arm 22 is engaged with an upper end 18a ofthe stem 18. The rocker arm 22 is in contact with an outer surface 24aof a lobed cam 24 operatively connected to a crankshaft (not shown) andthe opening and closing of the valve 16 is controlled by the rockingmovement of the rocker arm 22.

As illustrated in FIGS. 2 and 3, the lash adjuster 30 is comprisedgenerally of a cup-shaped body 31 having a blind bore 31a with a stepportion 31c. In the blind bore 31a there is slidably mounted a stepplunger 32 having an upper portion 32d and a lower portion 32e. Theexternal diameter of the upper portion 32d is smaller than the externaldiameter of the lower portion 32e.

A fluid pressure chamber 36 is formed between the closed end 31b of thebody 31 and the bottom wall 32a of the plunger 32. The pressure chamber36 is normally filled with a predetermined amount of hydraulic fluidsuch as silicone oil.

The plunger 32 is hollow and is provided with a reservoir chamber 35therein which is connected with the pressure chamber 36 through anaperture 37 provided in the bottom wall 32a of the plunger 32. A checkvalve in the form of a ball 38 is disposed in the pressure chamber 36 toclose the aperture 37. The ball 38 is biased by a spring 40 locatedwithin a cup-shaped retainer 39. The check valve 38 permits fluid flowonly from the reservoir chamber 35 to the pressure chamber 36. A returnspring 42 which biases the plunger 32 upwardly is disposed between theouter periphery of the retainer 39 and the closed end 31b of the body.The force of the spring 42 is larger than that of the spring 40.

An annular groove 33 is formed in the outer surface of the lower portion32e of the plunger 32. The annular groove 33 has a semi-circularcross-sectional configuration and communicates with the reservoirchamber 35 within the plunger 32 through four radially extendingpassages 34.

The lower portion 32e of the plunger 32 is also provided with an outerperipheral groove 32c above the semi-circular groove 33 in the axialdirection. The outer peripheral groove 32c is fitted with a syntheticrubber O-ring 45. The inner surface of the body 31 and the O-ring 45 arein fluid tight engagement with each other. An annular leakage clearance46 is provided between the inner surface of the body 31 and the outersurface of the lower portion 32e below the O-ring 45 through which thesilicone oil from the pressure chamber 36 will pass to the reservoirchamber 35. The leakage clearance 46 is required to be very precise andthe surfaces defining the clearance must be finished very carefullysince the quantity of the oil passing through the leakage clearance 46is very small. An elastic synthetic rubber bag 43 is disposed within thereservoir chamber 35. The bag 43 has a tubular configuration with oneend closed and the other end is provided with an annular outer flange43a which is fitted into an inner groove 32b provided at the opened endof the plunger 32. In order to prevent the bag 43 from withdrawing fromthe plunger 32, a metal ring 44 is disposed in the opening of the bag43. A flexible portion 43b of the bag 43 is always in contact with thesurface of the oil in the reservoir chamber 35 and changes shape thereofin accordance with the variations of the volume of oil. The interior 43cof the bag 43 is disposed in communication with the atmosphere.

The fulcrum 47 is comprised of an upper portion 47a, a middle portion47b and a sleeve 49 formed integrally with each other. The upper portion47a has a convex-spherical configuration and is engaged with acomplimentary concave spherical portion 22b provided at one end of therocker arm 22. The middle portion 47b is provided with passages 48through which the interior 43c of the bag 43 will communicate with theatmosphere. The sleeve 49 extends downwardly and is fitted between thebody 31 and the upper portion 32d of the plunger 32. The clearance C1between the outer surface of the sleeve 49 and the inner surface of thebody 31 is smaller than the clearance C2 formed between the innersurface of the sleeve 49 and the outer surface of the upper portion 32dof the plunger 32.

The plunger 32 is biased in the upward direction by the spring 42 andthe fulcrum 47 is biased in the downward direction by the rocker arm 22.Consequently, the lower end of the sleeve 49 is disposed in abutmentwith shoulder 32f of the plunger 32 so that the fulcrum 47 and theplunger 32 move as a unit. The upward movement of the fulcrum 47 and theplunger 32 is limited by an inverted cup-shaped member 50 disposed atthe open end of the body 31 and the downward movement of the fulcrum 47and the plunger 32 is limited by the stepped portion 31c of the body 31.

When the engine is started, the rocker arm 22 rotates in response to therotation of the cam 24 counterclockwise about the fulcrum 47 and thestem 18 is moved downwardly against the valve spring 20 thereby openingthe valve 16. The load of the valve spring 20 is increased so that thereaction force of the valve spring 20 is transmitted to the rocker arm22. The reaction force rotates the rocker arm 22 in the clockwisedirection about the point at which the rocker arm 22 and the cam 24 arein abutment with each other. Thus, the fulcrum 47 will be presseddownwardly so that the oil pressure within the pressure chamber 36 willbe increased and the ball 38 seated on the valve seat 41. A very smallamount of oil will then be leaked from the pressure chamber 36 to thereservoir chamber 35 through the leakage clearance 46, the semi-circulargroove 33 and the passages 34.

In response to further rotation of the cam 24, the stem 18 will be movedupwardly by the valve spring 20 and at the same time the rocker arm 22will rotate clockwise about the fulcrum 47. At this time, since the loadof the valve spring 20 becomes nearly 0, no downward force is applied tothe fulcrum 47 and the plunger 32 is moved upwardly relative to the body31. Consequently, the oil pressure in the pressure chamber 36 isdecreased and the ball 38 is released from the seat 41 against the forceof the spring 40 whereby the oil in the reservoir chamber 35 can passinto the pressure chamber 36 through the hole 37. Accordingly, the lashadjuster 32 is returned to the original length thereof.

When the downward force is applied to the fulcrum from the rocker arm22, the thrust force which is a horizontal component of the downwardforce is simultaneously applied to the fulcrum 47 and the plunger 32.Since the fulcrum 47 and the plunger 32 are not integral with each otherand the clearance C1 is smaller than the clearance C2, the outer surfaceof the sleeve 49 and the inner surface of the body 31 are placed incontact with each other by most of the thrust force. By the presence ofthe lubricating oil in the clearance C1, the inner surface of the body31 and the outer surface of the sleeve 49 are prevented from frictionalwear while the inner surface of the body 31 and the outer surface of theplunger are not brought into contact with each other. Accordingly, theoperating accuracy of the lash adjuster will be maintained. Furthermore,since the annular groove 33 is provided with a semi-circularcross-section, air will not remain in the annular groove when the lashadjuster 30 is assembled.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A self-contained lash adjuster comprising a bodyhaving an axially extending blind bore therein with an opening at oneend and a closed wall at the other end, a plunger slidably mounted insaid blind bore, a reservoir chamber located in said plunger, a pressurechamber disposed between said plunger and said closed wall of said body,a check valve for allowing fluid flow only from said reservoir chamberto said pressure chamber through an aperture in said plunger, a returnspring disposed between said closed wall of said body and said plungerto bias said plunger in the direction of said opening of said body, aleakage clearance between the inner surface of said body and the outersurface of said plunger, an annular groove provided on said outersurface of said plunger, radial passage means extending through saidplunger in communication with said groove to connect said leakageclearance to said reservoir chamber, a transmitting member slidablyinserted between the inside of said body and the outside of said plungeradjacent the opening at one end of the body, sealing means providing aseal between said plunger and said body intermediate said groove andsaid transmitting member, said one end of said transmitting memberdisposed in engagement with a shoulder portion of said plunger, atubular elastic bag fixed to said plunger within said reservoir chamberwith the closed end thereof being normally disposed in contact withfluid in said reservoir chamber and the interior of said bag beingdisposed in communication with the atmosphere, said closed end of saidbag extending past said radial passage means, and the clearance betweenthe inner surface of said body and the outer surface of saidtransmitting member being smaller than the clearance between the innersurface of said transmitting member and the outer surface of saidplunger.
 2. A self-contained lash adjuster as set forth in claim 1,wherein said transmitting member is comprised of a convex-sphericalshaped fulcrum portion, a middle portion and a sleeve portion formedintegrally with each other, said convex-spherical shaped fulcrum adaptedto engage one end of a rocker arm and said sleeve being interposedbetween said body and said plunger with the aforesaid clearances.
 3. Aself-contained lash adjuster as set forth in claim 1, wherein said firstgroove has a semi-circular cross-sectional configuration.